Reversible Pump Turbine and Guide Vane for the Reversible Pump Turbine

ABSTRACT

A reversible pump-turbine and also a guide vane for a reversible pump-turbine with a guide vane body, a pivot for rotating the guide vane body around an axis of rotation and two end faces. The guide vane body has a turbine leading edge facing the turbine flow and a turbine trailing edge facing away from the turbine flow, where the individual guide vanes come into contact with one another along closing edges when the wicket gate is closed, where the guide vanes each have two flow-guiding surfaces on either side of the axis of rotation and opposite one another that are limited by the two end faces. These two flow-guiding surfaces have different flow profiles.

BACKGROUND

The disclosed embodiments relate to a reversible pump-turbine with arunner and a wicket gate comprising a plurality of guide vanes, eachcomprising a guide vane body limited by end faces and a pivot forrotating the guide vane body round an axis of rotation. By rotating theguide vanes, the wicket gate can be opened and closed. The guide vanebody has a turbine leading edge facing the turbine flow and a turbinetrailing edge facing away from the turbine flow. When the wicket gate isclosed, the individual guide vanes come into contact with one anotheralong closing edges that are defined by the contact curves of adjacentguide vanes. Here, the guide vanes each have two flow-guiding surfaceson either side of the axis of rotation that are opposite one another andare limited by the two end faces.

The disclosure also relates to a guide vane for the reversiblepump-turbine.

The guide vanes in a reversible pump-turbine are arranged upstream ofthe runner in turbine operation and downstream of the runner in pumpoperation. They comprise a guide vane body and a pivot. All of the guidevanes together form the wicket gate. The guide vane body is rotateddirectly by turning the pivot round an axis of rotation. Hence, there isa specific wicket gate position in which adjacent guide vanes are incontact with one another along the closing edges when the guide vaneshave been installed. By adjusting the guide vanes, the pump-turbine canbe set from one operating point to another. Operating pump-turbines ismuch more complex than operating conventional turbines and requiresshort switch-over times between pump and turbine operation.

The switch-over times for a pump-turbine from pumping to turbineoperation are largely determined by the duration of the synchronisationprocess during which the rotational frequency of the hydraulic machineis synchronised with that of the electric power grid. If the no-loadcharacteristic curve shows turbine instability at the synchronisationpoint, the torque fluctuations this induces can cause significant delaysin successful synchronisation. Under such conditions, out-of-phasepressure and flow pulsations occur whose amplitudes can inducefluid-mechanical vibration in the hydraulic machine under resonanceconditions. This scenario presents a safety risk for the power plantoperator. The probability of such an occurrence can be reduced bypreventing turbine instabilities around the synchronisation point.

In the course of load rejection (as a result of a fault or power failurefor example), the runner accelerates to runaway speed and thepump-turbine undergoes transient operating conditions with differentpressure levels. In addition to runaway speed, the pressure increase inthe volute casing and the pressure drop in the draft tube are the maindesign parameters for a pumped-storage power plant. The stronger theturbine instability is at the given boundary conditions, the larger thepressure increase in the volute casing and the pressure drop in thedraft tube. In an emergency, the latter can cause so-called water-columnseparation in the draft tube, which generates large amounts of steam dueto cavitation formation. As the volume available inside the hydraulicmachine is almost constant, the axial thrust acting on the runnerincreases accordingly. A scenario of this kind normally leads toirreparable damage to the hydraulic machine and the powerhouse,representing a serious safety problem in the operation of pumped-storagepower plants.

As a result, a design that provides smooth and stable operation must beensured in addition to high efficiencies and good cavitationcharacteristics both in pumping and in turbine operation. Specificrequirements in terms of operating stability in the course of transientmanoeuvres are an essential part of every international tenderingprocess, and it is imperative that the manufacturers meet theserequirements.

It has been discovered that turbine instabilities caused by the flowinteract directly with the wicket gate and can be influenced indifferent ways depending on the design of the guide vane. The occurrenceof turbine instabilities can generally be attributed to the existence ofrevolving, stable vortex structures in the vaneless space, that is tosay the space between the wicket gate and the runner. These vortexformations impede the turbine flow exiting from the wicket gate,increase losses in the pump-turbine, and ultimately cause unstableoperating conditions, which can cause corresponding pressure and flowpulsations and facilitate system excitation. In order to increase theturbine stability of pump-turbines, the revolving, stable vortexstructures in the vaneless space must be interrupted or destabilised.

One possible method of stabilising operation is the so-called misalignedguide vane. Here, individual guide vanes are moved independently of theother guide vanes by means of individual servomotors. However, thiscontrol variant is expensive and entails a greater risk of failure forthe basic safety concept. As the closing procedures must continue tofunction properly, especially in the event of load rejection (due to afault, for example), misaligned guide vanes are not entirely accepted asa safety mechanism. There is a very clear trend here that is moving awayfrom this kind of actuator, particularly in future markets.

With a conventional guide vane, the flow profiles are typically paralleland congruent (see FIG. 1). Hence, the limiting surface of the guidevane body represents a cylindrical surface. The leading and trailingedges are straight lines (see FIG. 2).

In order to increase the hydraulic efficiency, guide vanes with adifferent shape are also used so that all flow profiles are congruent,but not parallel—see DE 199 59 227 A1 for example. The shape of theseguide vanes results essentially from identical flow profiles that aremisaligned in relation to one another.

AT 405 756 B discloses guide vanes with different flow profiles that areoptimized in terms of efficiency at full and at part load.

The state-of-the-art guide vane has the disadvantage that its design isnot flexible enough to be able to meet the demands of turbine stability,efficiency, cavitation characteristics and regulating range.

SUMMARY

The aim of the disclosed embodiments is thus to increase the turbinestability of pump-turbines during transient manoeuvres, i.e. during thesynchronisation process and in the event of load rejection. At the sametime, the turbine achieves a level of efficiency that is comparable tothat of a conventional guide vane. Similarly, the disclosed embodimentsdo not have a significant impact on the pump stability nor itscavitation characteristics.

Thus, provided herein are embodiments in which the flow-guiding surfacesof the respective guide vane form different flow profiles.

Hence, the guide vane body is not cylindrical and features a curvaturethat is created by the different shape of the flow profiles. Due to thisspecial shape of guide vane, the flow can be guided in such a way thatit specifically reaches the areas where the vortex structures occur,destabilises these vortex formations that are responsible for theturbine instability and thus significantly improves operating stability.

As the flow profiles differ from one another, i.e. they are notcongruent, a stabilizing effect can be achieved specifically in one areaand an “efficiency-maintaining” effect in another area of the guidevane.

It is preferable if the turbine trailing edge and the closing edge ofthe guide vane is curved at least once.

It is also feasible that the turbine trailing edge of the guide vaneand/or at least one closing edge of the guide vane has double curvature.

According to the invention, the flow profile in the mid-span section ofthe guide vane creates a different—in fact larger—absolute flow angle α₂of the absolute velocity of the turbine flow at the guide vane trailingedge in turbine direction, with regard to the related circumferentialcomponent of the absolute velocity of the turbine flow, than a flowprofile in the boundary area of the guide vane so the turbine flow inturbine direction leaves the guide vane body in the mid-span sectionwith a different flow angle α₂ than when it leaves the guide vane bodyin the boundary area.

Here, the mid-span section of the guide vane is approximately in thecentre between the two end faces of the guide vane.

Due to the fact that the flow angle α₂ is larger in the mid-spansection, the radially-acting momentum of the flow is increased towardsthe runner, destabilising the stable, revolving vortex formations in thevaneless space and subsequently achieving more stable operatingconditions in the reversible pump-turbine. Here, the boundary area isunderstood as being the area near the end faces of the guide vane body.

The inventor has noted that the undesirable vortex formations in thevaneless space can be destabilised as a result.

Intensified radially-acting momentum of the flow can be achieved in themid-span section of the guide vane, for example if the turbine trailingedge of the guide vane is curved in the mid-span section in a directionthat is perpendicular to a plane defined by the axis of rotation and aconnecting line between the turbine leading edge and the turbinetrailing edge. In this case, the guide vane is curved in the directionof the guide vane pressure side (in turbine direction).

Idealised, the guide vane angle corresponds to the absolute flow angleof the absolute velocity of the turbine flow along the guide vaneprofile (see FIG. 12). Idealised, the flow follows the guide vaneprofile.

Hence, according to the invention, the flow profile in the mid-spansection of the guide vane has a larger guide vane angle in the area ofthe turbine trailing edge than a flow profile in the boundary area ofthe guide vane so the turbine flow in turbine direction leaves the guidevane body at the mid-span section with a larger flow angle than if itleaves in the boundary area.

A favourable embodiment of the invention is characterised in that theposition of at least one flow profile is rotated around a straight linethat is disposed in parallel to the axis of rotation of the guide vane.The stabilising effect can be intensified again as a result of therotation.

A favourable development of the invention is characterised in that theradial position of at least one flow profile is misaligned in relationto a straight line. This makes the guide vane much more flexible in itsdesign.

An advantageous embodiment of the invention is characterised in that theturbine leading edge is curved at least once, whereby the turbinetrailing edge can also be curved at least once as an alternative or inaddition. With these measures, the highest efficiencies are achievedand, at the same time, the vortex structures responsible for the turbineinstability are destabilised.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail in the attached figures usingsome embodiment examples:

FIG. 1 shows a perspective view of a conventional guide vane accordingto the state of the art,

FIG. 2 shows a side view of a conventional guide vane according to FIG.1,

FIG. 3 shows a perspective view of a first embodiment of a guide vaneaccording to the disclosure,

FIG. 4 shows a perspective view of a second embodiment of a guide vaneaccording to the disclosure,

FIG. 5 shows a perspective view of a third embodiment of a guide vaneaccording to the disclosure,

FIG. 6 shows a perspective view of a fourth embodiment of a guide vaneaccording to the disclosure,

FIG. 7 shows a perspective view of a fifth embodiment of a guide vaneaccording to the disclosure,

FIG. 8 shows a side view of a guide vane as shown in FIG. 7,

FIG. 9 shows a perspective view (looking towards the turbine trailingedge) of a guide vane as shown in FIG. 7,

FIG. 10 shows two adjacent guide vanes of the wicket gate,

FIG. 11 shows a sectional view of a reversible pump-turbine, and

FIG. 12 shows the velocity triangles on the guide vanes.

DETAILED DESCRIPTION

A guide vane according to the state of the art is illustrated in FIG. 1.The same parts have the same reference numerals in the following. Thisguide vane has a guide vane axis of rotation 101, a pivot 102 and aguide vane body 103. The guide vane body 103 is defined by the flowprofiles 104, 105 and 106, which are parallel to one another andcongruent. Hence, the guide vane has a cymmetrical guide vane body 103.The same flow profiles 104, 105 and 106 define opposite flow-guidingsurfaces 119 and 120 that are limited by the two end faces 121, 122. Theturbine leading edge 107 and the turbine trailing edge 8 are straightlines. This shape of the flow profiles 104, 105 and 106 and of the guidevane body 103 is normally designed for maximum efficiency. The vortexstructures occurring (in the space between wicket gate and runner of thepump-turbine) cannot be destabilised with such a design.

The side view of the guide vane in FIG. 2 clearly shows that the turbineleading edge 107 and the turbine trailing edge 108 are straight linesand are aligned in parallel to the guide vane axis of rotation 101. Theguide vane body 103 is limited by a top flow profile 104 and a bottomflow profile 106, which form the end faces of the guide vane body 103.Therefore, every flow profile 105 between the top flow profile 104 andthe bottom flow profile 106, respectively, have the same shape. Theguide vane body 103 is defined by the flow profiles 104, 105 and 106,which are parallel to one another and congruent.

FIG. 3 shows a perspective view of a first variant of a guide vaneaccording to the invention. It corresponds largely to an embodiment ofthe prior art guide vane according to FIG. 1, with a guide vane axis ofrotation 1, a pivot 2, a guide vane body 3, a turbine leading edge 7 anda turbine trailing edge 8. The guide vane body 3 is also defined by theflow profiles 4, 5 and 6. Unlike the state of the art, flow profile 5 isnot congruent with flow profiles 4 and 6 and is generally located in arandom position between the end faces, 21 and 22. Flow profile 5, forexample, stabilises the flow, while flow profiles 4 and 6 maximize theefficiency. The connecting lines between the individual flow profiles 4,5 and 6 correspond advantageously to B-spline curves and form oppositeflow-guiding surfaces 19 and 20 that are limited by the two end faces21, 22. As a basic principle, one or both flow profiles 4, 6 at the endfaces 21, 22 of the guide vane body 3 can also be designed to stabilisethe flow and not be congruent with one another.

FIG. 4 illustrates a second embodiment of the disclosed guide vane.Here, too, flow profile 5 is not congruent with flow profiles 4 and 6.In addition, flow profile 5 is rotated in relation to a straight line 9.The straight line 9, for example, is disposed in parallel to the guidevane axis of rotation 1. Flow profile 5, for example, stabilises theflow, while flow profiles 4 and 6 maximize the efficiency. Theconnecting lines between the individual flow profiles 4, 5 and 6correspond advantageously to B-spline curves. As a result of thisrotation, the turbine leading edge 7 and turbine trailing edge 8 do notform straight lines, but curves.

FIG. 5 shows another embodiment of the disclosed guide vane, where theflow profile 5 here is not congruent with flow profiles 4 and 6 and islocated at a different position on the guide vane body 3 (axially orvertically displaced along a straight line 9 compared to the variant inFIG. 3). The straight line 9, for example, is positioned in parallel tothe guide vane axis of rotation 1. Flow profile 5, for example,stabilises the flow, while flow profiles 4 and 6 maximize theefficiency. The connecting lines between the individual flow profiles 4,5 and 6 correspond advantageously to B-spline curves.

FIG. 6 illustrates a guide vane body 3 that is structured analogously toFIG. 4. However, the flow-stabilising flow profile 5 is not rotatedaround a straight line here, but is positioned radially in relation to astraight line 9.

FIG. 7 now shows a variant of the invention that combines embodimentsfrom FIG. 5 and FIG. 6. Thus, the flow profile 5 is rotated around astraight line 9 and displaced radially in relation to the straight line9. The straight line 9, for example, is positioned in parallel to theguide vane axis of rotation 1. The turbine leading edge 7 and theturbine trailing edge 8 are curved. Flow profile 5, for example,stabilises the flow, while flow profiles 4 and 6 maximize theefficiency. The connecting lines between the individual flow profiles 4,5 and 6 correspond advantageously to B-spline curves.

FIG. 8 shows a side view of the variant according to FIG. 7. Thedisplacement and/or rotation and the curved turbine leading edge 7 andturbine trailing edge 8 are clearly visible here.

FIG. 9 shows a perspective view of the variant according to FIG. 7,looking towards the turbine trailing edge 8. Rotation of the flowprofile 5 compared to flow profiles 4 and 6 is particularly clear to seehere.

In FIG. 10, two adjacent guide vanes 13 of the wicket gate 16 are shownwhen the wicket gate 16 is closed. Here it is clear that the two guidevanes 13 are in contact along the closing edge 10. It is also clear thatthe closing edge 10 need not coincide with the turbine leading edge 7 orthe turbine trailing edge 8.

FIG. 11 shows a sectional view of a reversible pump-turbine 18. Inturbine operation, the water flows downstream from the volute casing 11through the stationary stay vanes 12 and then through the adjustableguide vanes 13 of the wicket gate 16. After this, the water passes therunner 14 and leaves the reversible pump-turbine 18 via the draft tube15.

The velocity triangles on the guide vanes 13 are shown in FIG. 12. Theturbine flow 17 is indicated by an arrow. The individual variables hererefer to the following parameters:

-   R₁ Radius of the guide vane leading edge in turbine direction to the    main machine axis-   C₁ Absolute velocity at the guide vane leading edge in turbine    direction-   C_(1u) Circumferential component of the absolute velocity at the    guide vane leading edge in turbine direction-   C_(1r) Radial component of the absolute velocity at the guide vane    leading edge in turbine direction-   R₂ Radius of the guide vane trailing edge in turbine direction to    the main machine axis-   C₂ Absolute velocity at the guide vane trailing edge in turbine    direction-   C_(2u) Circumferential component of the absolute velocity at the    guide vane trailing edge in turbine direction-   C_(2r) Radial component of the absolute velocity at the guide vane    trailing edge in turbine direction-   α₂ Absolute flow angle of the absolute velocity at the guide vane    trailing edge in turbine direction in relation to the corresponding    circumferential component of the absolute velocity C_(2u) at the    guide vane trailing edge in turbine direction, i.e. the included    angle between C₂ and C_(2u)

Where index 1 corresponds to the guide vane leading edge in turbinedirection and index 2 to the guide vane trailing edge in turbinedirection. The index u refers to the circumferential component and indexr to the radial component.

R₁ and R₂—and thus the guide vane leading and trailing edges—aredependent upon the opening angle of the guide vane.

Elements of the inventive embodiments described herein are identified asfollows:

-   1 Axis of rotation-   2 Pivot-   3 Guide vane body-   4 Flow profile-   5 Flow profile-   6 Flow profile-   7 Turbine leading edge-   8 Turbine trailing edge-   9 Straight line-   10 Closing edge-   11 Volute casing-   12 Stay vanes-   13 Guide vanes-   14 Runner-   15 Draft tube-   16 Wicket gate-   17 Turbine flow-   18 Pump-turbine-   19 Flow-guiding surface-   20 Flow-guiding surface-   21 End face-   22 End face

1-12. (canceled)
 13. A guide vane (13) that forms a wicket gate (16)with other guide vanes (13) for a pump-turbine (18), comprising: a guidevane body (3) having opposite end faces (21, 22) and being pivotableabout an axis of rotation (1) via a pivot (2), the guide vane body (3)having a turbine leading edge (7) facing a direction of turbine flow(17) and a turbine trailing edge (8) facing away from the directionturbine flow (17), wherein adjacent guide vanes (13) are configured tocontact one another along closing edges (10) when the wicket gate (16)is closed, the closing edges being defined by contact curves of adjacentguide vanes (13), the guide vane (13) has two flow-guiding surfaces (19,20) positioned on opposite sides of the axis of rotation (1) and beinglimited by the opposite end faces (21, 22), the flow-guiding surfaces(19, 20) forming different flow profiles (4, 5, 6), and wherein the flowprofile (5) in a mid-span section of the guide vane (13) has a largerguide vane angle toward the turbine trailing edge (8) than a flowprofile (4, 6) in a boundary area of the guide vane (13) proximate theopposite end faces (21, 22), such that the flow profile (5) in themid-span section of the guide vane (13) creates a larger absolute flowangle (α2) of absolute velocity (C2) of the turbine flow (17) at theguide vane trailing edge in turbine direction with regard to a relatedcircumferential component of the absolute velocity (C2 u) of the turbineflow (17), than a flow profile (4, 6) in the boundary area such that theturbine flow (17) in turbine direction leaves the guide vane body (3) inthe mid-span section with a larger flow angle (α2) than in the boundaryarea.
 14. The guide vane (13) according to claim 13, wherein the turbinetrailing edge (8) of the guide vane (13) is curved at least once. 15.The guide vane (13) according to claim 13, wherein the closing edge (10)of the guide vane (13) is curved at least once.
 16. The guide vane (13)according to claim 15, wherein the closing edge (10) of the guide vane(13) has a double curvature.
 17. The guide vane (13) according to claim14, wherein the turbine trailing edge (8) of the guide vane (13) has adouble curvature.
 18. The guide vane (13) according to claim 13, whereinthe turbine trailing edge (8) of the guide vane (13) is curved in themid-span section in a direction that is perpendicular to a plane definedby the axis of rotation (1) and a connecting line between the turbineleading edge (7) and the turbine trailing edge (8).
 19. The guide vane(13) according to claim 14, wherein the turbine trailing edge (8) of theguide vane (13) is curved in the mid-span section in a direction that isperpendicular to a plane defined by the axis of rotation (1) and aconnecting line between the turbine leading edge (7) and the turbinetrailing edge (8).
 20. The guide vane (13) according to claim 15,wherein the turbine trailing edge (8) of the guide vane (13) is curvedin the mid-span section in a direction that is perpendicular to a planedefined by the axis of rotation (1) and a connecting line between theturbine leading edge (7) and the turbine trailing edge (8).
 21. Theguide vane (13) according to claim 18, wherein the turbine trailing edge(8) of the guide vane (13) is curved in a direction of the guide vanepressure side.
 22. The guide vane (13) according to claim 13, whereinthe position of at least one flow profile (4, 5, 6) is rotated around astraight line (9) that is disposed parallel to the axis of rotation (1)of the guide vane (13).
 23. The guide vane (13) according to claim 14,wherein the position of at least one flow profile (4, 5, 6) is rotatedaround a straight line (9) that is disposed parallel to the axis ofrotation (1) of the guide vane (13).
 24. The guide vane (13) accordingto claim 15, wherein the position of at least one flow profile (4, 5, 6)is rotated around a straight line (9) that is disposed parallel to theaxis of rotation (1) of the guide vane (13).
 25. The guide vane (13)according to claim 13, wherein a radial position of at least one flowprofile (4, 5, 6) is misaligned in relation to a straight line (9) thatis disposed parallel to the axis of rotation (1).
 26. The guide vane(13) according to claim 13, wherein the turbine leading edge (7) iscurved at least once.
 27. The guide vane (13) according to claim 14,wherein the turbine leading edge (7) is curved at least once.
 28. Theguide vane (13) according to claim 15, wherein the turbine leading edge(7) is curved at least once.
 29. The guide vane (13) according to claim13, wherein the turbine trailing edge (8) of the guide vane (13) iscurved at least once such that an inflection point of the curve lies inthe mid-span section of the guide vane (13).
 30. The guide vane (13)according to claim 13, wherein the flow profiles (4) and (6) in therespective boundary area of the guide vane (13) are not congruent.
 31. Areversible pump-turbine (18) with a runner (14) and a wicket gate (16)comprising a plurality of the guide vanes (13) of claim
 13. 32. A guidevane (13) that forms a wicket gate (16) with other guide vanes (13) fora pump-turbine (18), comprising: a guide vane body (3) having oppositeend faces (21, 22) and being pivotable about an axis of rotation (1) viaa pivot (2), the guide vane body (3) having a turbine leading edge (7)facing a direction of turbine flow (17) and a turbine trailing edge (8)facing away from the direction turbine flow (17), wherein adjacent guidevanes (13) are configured to contact one another along closing edges(10) when the wicket gate (16) is closed, the closing edges beingdefined by contact curves of adjacent guide vanes (13), the guide vane(13) has two flow-guiding surfaces (19, 20) positioned on opposite sidesof the axis of rotation (1) and being limited by the opposite end faces(21, 22), the flow-guiding surfaces (19, 20) forming different flowprofiles (4, 5, 6), and wherein the flow profile (5) in a mid-spansection of the guide vane (13) intermediate the opposite end faces (21,22) has a larger guide vane angle toward the turbine trailing edge (8)than a flow profile (4, 6) in a boundary area of the guide vane (13)proximate the opposite end faces (21, 22), such that the flow profile(5) in the mid-span section of the guide vane (13) creates a largerabsolute flow angle (α2) of absolute velocity (C2) of the turbine flow(17) at the guide vane trailing edge in turbine direction with regard toa related circumferential component of the absolute velocity (C2 u) ofthe turbine flow (17), than a flow profile (4, 6) in the boundary areasuch that the turbine flow (17) in turbine direction leaves the guidevane body (3) in the mid-span section with a larger flow angle (α2) thanin the boundary area, the turbine trailing edge (8) and the closing edge(10) of the guide vane (13) are each curved at least once, the turbinetrailing edge (8) of the guide vane (13) is curved in the mid-spansection in a direction that is perpendicular to a plane defined by theaxis of rotation (1) and a connecting line between the turbine leadingedge (7) and the turbine trailing edge (8), and the turbine leading edge(7) is curved at least once.